WO2013150640A1

WO2013150640A1 - Electrolytic copper foil and method for manufacturing same

Info

Publication number: WO2013150640A1
Application number: PCT/JP2012/059442
Authority: WO
Inventors: 洋一皆川
Original assignee: Jx日鉱日石金属株式会社
Priority date: 2012-04-06
Filing date: 2012-04-06
Publication date: 2013-10-10

Abstract

An electrolytic copper foil characterized in that the difference in Vickers hardness (Hv) between the front and back of the electrolytic copper foil or the treated electrolytic copper foil is 10 or less. The electrolytic copper foil, characterized in that the amount of curvature of the electrolytic copper foil or the treated electrolytic copper foil is 1 mm or less. A method for manufacturing an electrolytic copper foil, characterized in comprising heating an electrolytic copper foil or a treated electrolytic copper foil at 130-155°C in an oven to remove distortion of the electrolytic copper foil or the treated electrolytic copper foil. The present invention relates to an electrolytic copper foil in which curvature due to thermal load is reduced, and to a method for manufacturing the same, and particularly addresses the problem of providing an electrolytic copper foil useful in a negative electrode collector for a secondary cell.

Description

Electrolytic copper foil and method for producing the same

The present invention relates to an electrolytic copper foil with reduced warpage due to a thermal load and a method for producing the same, and more particularly to an electrolytic copper foil useful for a secondary battery negative electrode current collector.

Electrolytic copper foil produced by electroplating greatly contributes to the development of electrical and electronic industries, and is indispensable as a printed circuit material and secondary battery negative electrode current collector. The manufacturing history of the electrolytic copper foil is old (see Patent Document 1 and Patent Document 2), but recently its usefulness as a secondary battery negative electrode current collector has been reconfirmed.

An example of producing an electrolytic copper foil is as follows. For example, in an electrolytic cell, a titanium or stainless steel rotating drum having a diameter of about 3000 mm and a width of about 2500 mm and an electrode distance of about 5 mm around the drum are arranged. Deploy.
Copper, sulfuric acid, and glue are introduced into this electrolytic cell to form an electrolytic solution. Then, the linear velocity, the electrolyte solution temperature, and the current density are adjusted, copper is deposited on the surface of the rotating drum, the copper deposited on the surface of the rotating drum is peeled off, and a copper foil is continuously produced.

This electrolytic copper foil manufacturing method can reduce the manufacturing cost, and can manufacture from an extremely thin layer thickness of about several μm to a thick copper foil of about 70 μm, and one side of the electrolytic copper foil is moderate. Therefore, it has many advantages such as high adhesive strength with the resin.

In recent years, electrolytic copper foil has been used as a copper foil for negative electrode materials for in-vehicle batteries (lithium ion batteries). However, since the active material is applied on both sides, the drum surface and the deposited surface may have the same roughness and shape. It is desirable.
In a lithium ion secondary battery using a commercially available electrolytic copper foil as a negative electrode current collector, the battery characteristics, particularly the cycle characteristics in charge and discharge, were poor and could not be used. It has been found that the above-described problem is caused because a large unevenness is formed on one main surface of the electrolytic copper foil, and the difference in surface roughness between both main surfaces of the electrolytic copper foil is too large.

Until now, electrolytic copper foil has been mainly used for printed circuit boards and flexible substrates. In order to improve the adhesion to plastics (to achieve the anchor effect), the main surface of the electrolytic copper foil has large irregularities. Was forming. Therefore, when this electrolytic metal foil is used as a current collector of a non-aqueous electrolyte secondary battery, deformation along the active material surface does not occur sufficiently, the contact between the active material and the current collector is poor, and the capacity Deterioration and cycle characteristics were reduced (see Patent Document 3).

Therefore, in order to produce a low-roughness copper foil in which the roughness of the precipitation surface was suppressed, an additive was added to make an electrolytic copper foil. However, due to the influence of the additive, the internal stress of the copper layer increases immediately after the foil production, but the crystal structure of the copper layer is stabilized by releasing the internal stress. However, due to the release of the internal stress, a stress difference occurs between the two surfaces, causing a problem of warping to the precipitation surface side.

The production process of the negative electrode current collector is a process in which a slurry-like active material is applied to both sides of copper foil, dried, and then crimped by a roll press. When the copper foil warps to the deposition surface (M surface) side, in the active material coating process, the gap between the equipments is narrow, so that a problem arises that the copper foil comes into contact with the equipment to cause a problem. The conventional copper foil has a tendency to warp the M-plane, and has included a problem.

Japanese Patent Laid-Open No. 7-188969 JP 2004-107786 A Japanese Patent No. 3742144

The present invention investigates the cause of warping of copper foil that occurs when conventional electrolytic copper foil is used, and electrolytic copper foil, particularly secondary battery negative electrode, in which warpage due to thermal load is reduced to solve this cause It is an object of the present invention to provide an electrolytic copper foil useful for a current collector and a method for producing the same.

It has been found that the main cause of warping of the copper foil that occurs when the electrolytic copper foil is used is that the difference in hardness (Vickers hardness) on both sides of the electrolytic copper foil is large. From this knowledge, the present invention provides the following inventions.

1) The electrolytic copper foil, wherein the difference in Vickers hardness (Hv) between the front and back surfaces of the electrolytic copper foil or the treated electrolytic copper foil is 10 or less.
2) The amount of warp of the electrolytic copper foil or the treated electrolytic copper foil is 1 mm or less, 3) The electrolytic copper foil according to the above 1), wherein the tensile strength of the electrolytic copper foil or the treated electrolytic copper foil is 30- The electrolytic copper foil according to the above 1) or 2), characterized in that it is 40 kg / mm ^2. 4) The elongation of the electrolytic copper foil or the electrolytic copper foil after treatment is 10 to 15%. 4) The electrolytic copper foil according to any one of 1) to 4) above, which is a copper foil for a secondary battery negative electrode current collector. Foil

6) Electrolytic copper foil or treated electrolytic copper foil is heated in an oven at 130 to 155 ° C. to remove the distortion of the electrolytic copper foil or the treated electrolytic copper foil. Method.
7) The method for producing an electrolytic copper foil according to 6) above, wherein the difference in Vickers hardness (Hv) between the front and back surfaces of the electrolytic copper foil or the treated electrolytic copper foil is 10 or less by removing strain. 8) The electrolysis according to 6) or 7) above, wherein the warping amount of the electrolytic copper foil after heat load at 130 to 155 ° C. or the electrolytic copper foil after treatment is 1 mm or less by removing strain Any of 6) to 8) above, wherein the tensile strength of the electrolytic copper foil after heat load at 130 to 155 ° C. or the electrolytic copper foil after treatment is 30 to 40 kg / mm ^2. 10) The electrolytic copper foil production method according to any one of 6) to 9) above, wherein the elongation after a heat load at 130 to 155 ° C. is 10 to 15%. Copper foil manufacturing method

The present invention investigates the cause of warping of the copper foil that occurs when the electrolytic copper foil is used, and as a solution to this, by reducing the difference in hardness between both sides of the electrolytic copper foil, It is possible to obtain a reduced electrolytic copper foil, and in particular, it has an excellent effect of providing an electrolytic copper foil useful for a secondary battery negative electrode current collector.

It is a schematic explanatory drawing of the typical manufacturing apparatus which manufactures an electrolytic copper foil.

The present invention provides an electrolytic copper foil in which the difference in Vickers hardness (Hv) between the front and back surfaces of the electrolytic copper foil or the treated electrolytic copper foil is 10 or less, as described above. The main cause of warping of copper foil (a phenomenon of warping on the deposition surface (M surface) side of the electrolytic copper foil) that occurs when using copper is largely due to a large difference in hardness (Vickers hardness) on both surfaces of the electrolytic copper foil. it is conceivable that.
In order to reduce this difference, it became possible to reduce the difference in both-side hardness of the electrolytic copper foil by increasing the oven temperature and increasing the heat application in the oven drying process performed in the treatment process. This is the result of the release of the strain inside the copper foil by heating, which makes it possible to greatly reduce the amount of warpage.

As mentioned above, there is a drying process in the oven after the treatment. By using this drying process, the electrolytic copper foil can be heated to a predetermined temperature to reduce the difference between the front and back of the Vickers hardness of the electrolytic copper foil. Is possible. However, even when the treatment is not performed, and even when the drying process by the oven is not attached after the treatment, the same purpose can be achieved by performing the heat treatment by the same oven on the electrolytic copper foil itself.

By reducing the difference between the front and back of the Vickers hardness of the electrolytic copper foil of the present invention, the warp amount of the electrolytic copper foil or the electrolytic copper foil after treatment is 1 mm or less even if there is a subsequent heat load of 130 to 155 ° C. it can. This amount of warpage is a problem in the negative electrode current collector preparation process, that is, a process in which a slurry-like active material is applied to both sides of a copper foil, dried, and then crimped by a roll press (in the active material application process, the spacing of equipment Therefore, there is no problem that the copper foil comes into contact with the equipment to cause a problem.

Also, by such heat treatment, the tensile strength of the electrolytic copper foil after heat load at 130 to 155 ° C. or the electrolytic copper foil after treatment (thickness 12 μm) can be maintained at 30 to 40 kg / mm ^2. . It should be understood that the tensile strength of the electrolytic copper foil is not limited to this value because it changes depending on the electrolytic conditions and the thickness of the copper foil.

Further, by the above heat treatment, the elongation of the electrolytic copper foil after a heat load of 130 to 155 ° C. or the electrolytic copper foil after treatment (12 μm thickness) can be made 10 to 15%. Usually, the preferred elongation to be performed is in the range of 12-14%. Similarly, it is to be understood that the elongation of the electrolytic copper foil is not limited to this value because it changes depending on the electrolytic conditions and the thickness of the copper foil.
From the above, electrolysis useful for the secondary battery negative electrode current collector can be obtained.

As a specific method for removing the distortion of the electrolytic copper foil or the treated electrolytic copper foil, the electrolytic copper foil or the treated electrolytic copper foil is heat-treated in an oven at 130 to 155 ° C. for about 5 to 15 seconds. Can be obtained. When the temperature is less than 130 ° C., the difference in Vickers hardness (Hv) between the front and back surfaces of the electrolytic copper foil or the treated copper foil cannot be reduced to 10 or less. The amount of warpage of the electrolytic copper foil or the electrolytic copper foil after treatment cannot be 1 mm or less.

When heat treatment is performed at a temperature exceeding 155 ° C., the difference in Vickers hardness (Hv) between the front and back surfaces of the electrolytic copper foil can be made 10 or less, but when the surface of the electrolytic copper foil is oxidized and discolored, Since there is a possibility that the inside of the copper foil is recrystallized, it cannot be said that it is preferable, and the heat treatment temperature and the heat treatment time are also limited. Therefore, it can be said that the above range is desirable.

Further, the above heat treatment removes the strain, the tensile strength of the electrolytic copper foil after heat load at 130 to 155 ° C. or the electrolytic copper foil after treatment (12 μm thickness) is 30 to 40 kg / mm ² , and the elongation is 10 Can be maintained at ~ 15%.

The electrolytic copper foil of the present invention can be produced by an electrolytic method using a sulfuric acid-based copper electrolyte using an electrolytic copper foil production apparatus as shown in FIG. The present invention relates to a conventional electrolytic copper in which, for example, a rotating drum made of titanium or stainless steel having a diameter of about 3000 mm and a width of about 2500 mm and an electrode is disposed around the drum with an inter-electrode distance of about 5 mm. It can manufacture using a foil manufacturing apparatus. The example of this apparatus is an example and there is no restriction | limiting in particular in the specification of an apparatus.

In this electrolytic cell, copper concentration: 80 to 110 g / L, sulfuric acid concentration: 70 to 110 g / L, glue concentration: 2.0 to 10.0 ppm, and appropriate additives are introduced to obtain an electrolytic solution.
Then, the linear velocity was adjusted to 1.5 to 5.0 m / s, the electrolyte temperature was adjusted to 60 to 65 ° C., and the current density was adjusted to 60 to 120 A / dm ² to deposit copper on the surface of the rotating drum. The copper deposited on the surface of the film is peeled off to continuously produce a copper foil.
Usually, electrolysis is performed at an electrolyte temperature of 60 to 65 ° C. and a current density of 60 to 120 A / dm ² . This is a suitable condition for obtaining an electrolytic copper foil having the above characteristics. However, it is not necessary to be fixed (restricted) to this condition, but adjustment of the electrolyte temperature is important. Details will be described in Examples and Comparative Examples.

Treating and roughening treatments can be applied to the surface or back surface of this electrolysis, or both surfaces as necessary. The treatment process is normally performed, but may be omitted if necessary.
For the roughening treatment, for example, the average surface roughness Ra can be set to 0.04 to 0.20 μm. In this case, the reason why the lower limit of the average surface roughness Ra is 0.04 μm is to form fine particles and improve the adhesion.

This makes it possible, for example, to apply as much active material as possible for the secondary battery and increase the electric capacity of the battery. On the other hand, the reason for setting the upper limit to 0.20 μm is to reduce variation in weight thickness. Thereby, for example, the charge / discharge characteristics of the secondary battery can be improved. These surface roughnesses show an example and can be appropriately adjusted according to the use of the electrolytic copper foil.

Further, taking the copper foil for a negative electrode current collector for a secondary battery as an example, it is desirable that the average diameter of the roughened particles on the roughened surface be 0.1 to 0.4 μm. It is desired that the roughened particles are fine particles and the fine particles are more uniform. Similarly to the above, this is a preferable mode for improving the adhesion of the battery active material and applying as much active material as possible to increase the electric capacity of the battery.

Moreover, it is desirable that the maximum height of the roughened layer in the copper foil for the negative electrode current collector for the secondary battery is 0.2 μm or less. This is also a preferable mode for reducing the thickness variation of the roughening treatment layer, improving the adhesion of the battery active material, and increasing the electric capacity of the battery by applying as much active material as possible. The present invention can be managed and achieved based on an index that makes the thickness of the roughened particles 0.2 μm or less.

The copper foil for a negative electrode current collector for a secondary battery can form one type of plating of copper, cobalt, nickel or two or more types of alloy plating as roughening particles. Usually, roughened particles are formed by three-part alloy plating of copper, cobalt, and nickel. Furthermore, the copper foil for the negative electrode current collector for the secondary battery has a cobalt-nickel alloy plating layer on the roughened surface on both the front and back sides of the rolled copper alloy foil in order to improve heat resistance and weather resistance (corrosion resistance). It is a desirable element to form one or more rust-proofing layers or heat-resistant layers and / or silane coupling layers selected from zinc-nickel alloy plating layers and chromate layers.

As described above, the copper foil for a negative electrode current collector for a secondary battery of the present invention can reduce the thickness variation in the copper foil width direction of the rolled copper alloy foil after the front and back surface roughening treatment to 0.5% or less. An excellent copper foil for a negative electrode current collector for a secondary battery can be provided.

The roughening treatment on the copper foil for the secondary battery negative electrode current collector of the present invention can be performed, for example, copper roughening treatment or copper-cobalt-nickel alloy plating treatment.
For example, the copper roughening treatment is as follows.
Copper roughening treatment Cu: 10 to 25 g / L
H ₂ SO ₄ : 20 to 100 g / L
Temperature: 20-40 ° C
Dk: 30 to 70 A / dm ²
Time: 1-5 seconds

The roughening treatment by the copper-cobalt-nickel alloy plating treatment is as follows. By electrolytic plating, the amount of deposition is carried out to form a ternary alloy layer such that 15 ~ 40mg / dm ² of copper -100 ~ 3000μg / dm ² of cobalt -100 ~ 500μg / dm ² of nickel. This ternary alloy layer also has heat resistance.

The general bath and plating conditions for forming such ternary copper-cobalt-nickel alloy plating are as follows.
(Copper-cobalt-nickel alloy plating)
Cu: 10 to 20 g / liter Co: 1 to 10 g / liter Ni: 1 to 10 g / liter pH: 1 to 4
Temperature: 30-50 ° C
Current density D _k : 20 to 50 A / dm ²
Time: 1-5 seconds

After the roughening treatment, a cobalt-nickel alloy plating layer can be formed on the roughened surface. The cobalt-nickel alloy plating layer has a cobalt adhesion amount of 200 to 3000 μg / dm ² and a cobalt ratio of 60 to 70 mass%. This treatment can be regarded as a kind of rust prevention treatment in a broad sense.

The conditions for the cobalt-nickel alloy plating are as follows.
(Cobalt-nickel alloy plating)
Co: 1-20 g / liter Ni: 1-20 g / liter pH: 1.5-3.5
Temperature: 30-80 ° C
Current density D _k : 1.0 to 20.0 A / dm ²
Time: 0.5-4 seconds

A zinc-nickel alloy plating layer can be further formed on the cobalt-nickel alloy plating. The total amount of the zinc-nickel alloy plating layer is 150 to 500 μg / dm ² and the nickel ratio is 16 to 40% by mass. This has the role of a heat and rust preventive layer.

The conditions for zinc-nickel alloy plating are as follows.
(Zinc-nickel alloy plating)
Zn: 0-30 g / liter Ni: 0-25 g / liter pH: 3-4
Temperature: 40-50 ° C
Current density D _k : 0.5 to 5 A / dm ²
Time: 1 to 3 seconds

After this, if necessary, the following rust prevention treatment can be performed. A preferable antirust treatment is a coating treatment of chromium oxide alone or a mixture coating treatment of chromium oxide and zinc / zinc oxide. Chromium oxide and zinc / zinc oxide mixture film treatment means zinc or zinc oxide comprising zinc oxide and chromium oxide by electroplating using a plating bath containing zinc salt or zinc oxide and chromate. It is the process which coat | covers the antirust layer of a chromium group mixture.

As the plating bath, typically, at least one kind of dichromate such as K ₂ Cr ₂ O ₇ and Na ₂ Cr ₂ O ₇ and CrO ₃ and a water-soluble zinc salt such as ZnO ₄ and ZnSO ₄ · 7H are used. A mixed aqueous solution of at least one kind such as ₂ O and an alkali hydroxide is used. A typical plating bath composition and electrolysis conditions are as follows. The copper foil thus obtained has excellent heat resistance peel strength, oxidation resistance and hydrochloric acid resistance.

(Chromium rust prevention treatment)
K ₂ Cr ₂ O ₇ (Na ₂ Cr ₂ O ₇ or CrO ₃ ): 2 to 10 g / liter NaOH or KOH: 10 to 50 g / liter ZnO or ZnSO ₄ · 7H ₂ O: 0.05 to 10 g / liter pH: 3-13
Bath temperature: 20-80 ° C
Current density D _k : 0.05 to 5 A / dm ²
Time: 5-30 seconds Anode: Pt—Ti plate, stainless steel plate, etc. Chromium oxide requires a coating amount of 15 μg / dm ² or more, and zinc requires a coating amount of 30 μg / dm ² or more.

Finally, if necessary, silane treatment is performed by applying a silane coupling agent to at least the roughened surface on the rust preventive layer, mainly for the purpose of improving the adhesion between the copper foil and the resin substrate. Examples of the silane coupling agent used for the silane treatment include olefin silane, epoxy silane, acrylic silane, amino silane, and mercapto silane, and these can be appropriately selected and used. .

Application method may be any of spraying a silane coupling agent solution by spraying, coating with a coater, dipping, pouring and the like. For example, Japanese Patent Publication No. 60-15654 describes that the adhesion between a copper foil and a resin substrate is improved by subjecting the rough surface of the copper foil to a chromate treatment followed by a silane coupling agent treatment. . Refer to this for details. Thereafter, if necessary, an annealing treatment may be performed for the purpose of improving the ductility of the copper foil.

As for the above, an additional surface treatment layer to the electrolytic copper foil of the present invention, which is mainly applied to the negative electrode current collector for secondary batteries, has been described, but these are arbitrarily selected according to the use of the electrolytic copper foil. Needless to say, it can be applied. The present invention includes all of these.

Hereinafter, description will be made based on examples and comparative examples. In addition, a present Example is an example to the last, and is not restrict | limited only to this example. That is, it includes other aspects or modifications included in the present invention.

In the electrolytic cell, a titanium rotating drum having a diameter of about 3133 mm and a width of 2476.5 mm and an electrode distance of about 5 mm were arranged around the drum.
The electrolytic solution was 85 g / L copper, 75 g / L sulfuric acid, 60 mg / L chloride ion, 3-10 ppm bis- (3-sulfopropyl) -disulfide sodium salt, and 2-20 ppm nitride-containing organic compound.
The electrolyte temperature was 57 ° C., the electrolyte linear velocity was 1.0 m / min, and the current density was 50 A / dm ² . Copper was deposited on the surface of the rotating drum, and the copper deposited on the surface of the rotating drum was peeled off to continuously produce a copper foil. The foil thickness of the electrolytic copper foil was 9.5 to 12.5 μm.

The copper foil was subjected to a surface oxidation preventing treatment so that the chromium adhesion amount was in the range of 2.6 to 4.0 mg / m ² and dried in an oven. Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 shown below are the same except for the processing differences shown in Table 1. The heating time in the oven is about 10 seconds in all cases.

Example 1
In Example 1, the heat treatment temperature of the electrolytic copper foil treated by the oven is 140 ° C. There was no surface discoloration due to oxidation after a heat load of 140 ° C. The Vickers hardness (Hv) on the drum surface side of the electrolytic copper foil was 94, and the Vickers hardness (Hv) of the precipitation surface on the opposite side was 85, the difference being 9, which satisfied the conditions of the present invention. Further, the amount of warpage was 0.7 mm, and the amount of warpage was small, achieving the object of the present invention. The results are shown in Table 1 above.
The tensile strength of Example 1 was 34.8 kgf / mm ² and the elongation was 13.3%. These also achieved the object of the present invention. The results are shown in Table 2.

(Comparative Example 1)
In Comparative Example 1, the treatment was not performed. Since no rust prevention treatment was applied, the surface was discolored due to oxidation. The Vickers hardness (Hv) on the drum surface side of the electrolytic copper foil was 105, and the Vickers hardness (Hv) of the precipitation surface on the opposite side was 79, the difference being 26, which did not satisfy the conditions of the present invention. Further, the amount of warpage was 1.5 mm, the amount of warpage was large, and the object of the present invention was not satisfied. The results are similarly shown in Table 1 above. Further, the tensile strength of Comparative Example 1 was 35.5 kgf / mm ² and the elongation was 13.3%, which were within the range of the conditions of the present invention. The results are shown in Table 2.

(Example 2)
The heat treatment temperature of the electrolytic copper foil treated with the oven of Example 2 is 150 ° C. There was no surface discoloration due to oxidation after a heat load of 150 ° C. The Vickers hardness (Hv) on the drum surface side of the electrolytic copper foil was 92, and the Vickers hardness (Hv) of the precipitation surface on the opposite side was 83, and the difference was 9, which satisfied the conditions of the present invention. Moreover, the amount of warpage was 0.4 mm, the amount of warpage was small, and the object of the present invention was achieved.
The results are shown in Table 1 above. Moreover, the tensile strength of Example 2 was 34.6 kgf / mm < ² >, and elongation was 13.6%, These also achieved the objective of this invention. The results are shown in Table 2.

(Comparative Example 2)
About the comparative example 2, it is a case where the treated electrolytic copper foil is heat-processed at 120 degreeC in oven. As a result, there was no surface discoloration due to oxidation after 120 ° C. heat load. The Vickers hardness (Hv) on the drum surface side of the electrolytic copper foil was 103, and the Vickers hardness (Hv) of the precipitation surface on the opposite side was 80. The difference was 23, which did not satisfy the conditions of the present invention. Further, the amount of warpage was 1.5 mm, the amount of warpage was large, and the object of the present invention was not satisfied. This was considered because the heat treatment was as low as 120 ° C.
The results are similarly shown in Table 1 above. Moreover, the tensile strength of the comparative example 2 was 35.5 kgf / mm < ² >, and elongation was 13.4%, and these were in the range of the conditions of this invention. The results are shown in Table 2.

(Comparative Example 3)
Comparative Example 3 is a case where the treated electrolytic copper foil was heat-treated at 160 ° C. in an oven. As a result, after heat load at 160 ° C., discoloration of the surface due to oxidation was observed. The Vickers hardness (Hv) on the drum surface side of the electrolytic copper foil is 92, and the Vickers hardness (Hv) of the precipitation surface on the opposite side is 85, the difference being 7, which satisfies the conditions of the present invention, and the amount of warpage Was 0.5 mm, and the amount of warpage was small, satisfying the object of the present invention. However, since the heat treatment was as high as 160 ° C., discoloration occurred, which was not preferable.
The results are similarly shown in Table 1 above. Moreover, the tensile strength of the comparative example 2 was 34.7 kgf / mm < ² >, and elongation was 13.2%, About these, it was in the range of the conditions of this invention. The results are shown in Table 2.

As a result, Vickers hardness is higher on the drum surface under all conditions. The reason is that stress release on the drum surface is suppressed, and the crystal size is smaller than that of the precipitation surface, so that it is considered that there is a difference in hardness. However, when the electrolytic copper foil or the treated electrolytic copper foil is heat-treated in an oven at 130 to 155 ° C., the Vickers hardness (Hv) between the drum surface side of the electrolytic copper foil and the opposite deposition surface is obtained. This can be said to be an effective condition that can reduce the difference between the two and reduce the amount of warpage. Even when the thickness of the electrolytic copper foil was changed, the same results as in the above Examples and Comparative Examples could be obtained.

As described above, heat treatment is performed at 130 to 155 ° C. in an oven, so that the amount of heat is larger than that of normal drying. However, the amount of heat is not high enough to recrystallize, and there is no significant difference between high tension and elongation. The conditions of the invention were met.

The present invention investigates the cause of warping of the copper foil that occurs when the electrolytic copper foil is used, and as a solution to this, by reducing the difference in hardness between both sides of the electrolytic copper foil, It is possible to obtain a reduced electrolytic copper foil, and it is possible to provide an electrolytic copper foil that is particularly useful for a secondary battery negative electrode current collector.

Claims

An electrolytic copper foil characterized in that the difference in Vickers hardness (Hv) between the front and back surfaces of the electrolytic copper foil or the treated electrolytic copper foil is 10 or less.
2. The electrolytic copper foil according to claim 1, wherein the amount of warpage of the electrolytic copper foil or the electrolytic copper foil after treatment is 1 mm or less.
3. The electrolytic copper foil according to claim 1, wherein the electrolytic copper foil or the electrolytic copper foil after treatment has a tensile strength of 30 to 40 kg / mm 2 .
The electrolytic copper foil according to any one of claims 1 to 3, wherein an elongation of the electrolytic copper foil or the electrolytic copper foil after treatment is 10 to 15%.
The electrolytic copper foil according to any one of claims 1 to 4, which is a copper foil for a secondary battery negative electrode current collector.
An electrolytic copper foil or a treated electrolytic copper foil is heated in an oven at 130 to 155 ° C. to remove distortion of the electrolytic copper foil or the treated electrolytic copper foil.
The method for producing an electrolytic copper foil according to claim 6, wherein the difference in Vickers hardness (Hv) between the front and back surfaces of the electrolytic copper foil or the treated electrolytic copper foil is 10 or less by removing the strain.
The electrolytic copper foil according to claim 6 or 7, wherein the warping amount of the electrolytic copper foil after heat load at 130 to 155 ° C or the electrolytic copper foil after treatment is 1 mm or less by removing strain. Production method.
The electrolytic copper foil according to any one of claims 6 to 8, wherein the tensile strength of the electrolytic copper foil after heat load at 130 to 155 ° C or the electrolytic copper foil after treatment is set to 30 to 40 kg / mm 2. Manufacturing method.
The method for producing an electrolytic copper foil according to any one of claims 6 to 9, wherein the elongation after a heat load of 130 to 155 ° C is 10 to 15%.